1. Field of the Invention
The present invention relates generally to a method and apparatus for treating a fluid, such as the sterilization of water, or a material therein using acoustic energy in the form of cavitation, large amplitude acoustic waves, and/or water hammer, generated by the rapid condensation of steam which is injected into the fluid. More particularly, it concerns a method and apparatus for selectively injecting steam into a reflector member disposed in the fluid which is shaped to focus and direct the acoustic energy at a target zone within the chamber where the acoustic waves converge causing secondary cavitation, the chamber also being shaped to focus the acoustic energy.
2. Background Art
A growing number of municipalities both inside and outside the United States are constrained to using drinking water supplies that come from local rivers, lakes, and reservoirs that contain significant amounts of hazardous micro-organismns. In many cases conventional chemical detoxification methods result in undesirable amounts of chlorine and chlorine byproducts in the treated water. Consequently, the municipal drinking water supply is characterized by water that is unpalatable as well as being a potential health problem. In recent years various non-chemical sonication schemes have been devised to replace or limit the use of chemicals in water treatment procedures.
These sonication schemes utilize high-amplitude ultrasonic sound waves to cause cavitation in a liquid. Cavitation occurs when the high-amplitude ultrasonic sound waves create gas-bubble cavities in the liquid. When the cavities collapse they produce intense localized pressures. This cavitation may be induced to destroy liquid-borne organisms, mix fluids or slurries, promote certain chemical reactions, and otherwise treat fluids or materials therein.
The high-amplitude ultrasonic sound waves are typically generated by electrically driven piezoelectric or magnetostrictive transducers. The transducers are usually directed into a static liquid tank or a tank in which the liquid is circulated in order to sterilize objects within the tank, such as surgical instruments, or to sterilize the fluid itself One disadvantage of transducers is that they are typically confined to small scale systems or batch processes.
Some larger scale systems for processing a continuous flow of water have been proposed. For example, U.S. Pat. No. 5,611,993, issued Mar. 18, 1997, to Babaev, discloses a method which uses various tank configurations and inlet and outlet locations to cause temporary pooling of the water while a transducer for transmitting a high frequency sound wave is directed at the pooled water. U.S. Pat. No. 4,086,057, issued Apr. 25, 1978, to Everett, discloses a free jet of water directed against an ultrasonic vibrating surface. One disadvantage with these systems is that they are not practical for large scale disinfection of a continuously flowing fluid. U.S. Pat. No. 5,611,993, issued Mar. 18, 1997, to Babaev, discloses a plurality of opposing transducers. One disadvantage with some of these systems is their use of a larger number of transducers which consequently utilize a larger amount of electricity to operate.
Other systems require additional processing steps to supplement the sonic process. For example, U.S. Pat. No. 5,466,425, issued Nov. 14, 1995, to Adams discloses a system utilizing an applied voltage, ultraviolet radiation, and high frequency. Similarly, U.S. Pat. No. 5,326,468, issued Jul. 5, 1994, to Cox, discloses cavitation induced by the pressure drop across a nozzle throat and subsequent ultraviolet radiation, ion exchange, and degassifying treatment. See also U.S. Pat. No. 5,494,585, issued Feb. 27, 1996, to Cox; and U.S. Pat. No. 5,393,417, issued Feb. 28, 1995, to Cox. One disadvantage of these systems is their reliance on secondary treatments. Another disadvantage is their continued use of trstems utilize a cavitation chamber. For example, U.S. Pat. No. 5,519,670, issued May 21, 1996, to Walter, discloses a cavitation chamber in which acoustic pulses are generated by repeatedly closing a valve, creating water hammer. The water hammer propagates into the cavitation chamber through a diaphragm. See also U.S. Pat. No. 5,508,975, issued Apr. 16, 1996, to Walter. One problem with this type of system is that repeatedly closing the valve fatigues the system components. Another problem with this type of system is the use of a diaphragm which may become fatigued and fail. Another problem with many systems is the complexity and number of components subject to failure.
Another problem with many of the above systems is that the acoustic energy generated is inefficiently used. For example, the acoustic energy is indirectly propagated from a pipe system into a cavitation chamber. Other systems merely direct the transducer in the desired direction. U.S. Pat. No. 5,459,699, issued Oct. 17, 1995, to Walter, discloses a flexible, indented pipe to direct some of the water hammer in the pipe into a surrounding fluid. Most of the acoustic energy in these systems randomly propagates through the system.
Although most systems utilize transducers to create cavitation, some systems utilize the pressure drop across a nozzle to induce cavitation downstream of the nozzle throat. See U.S. Pat. Nos. 5,326, 468; 5,494,585; and 5,393,417. Traditionally, this type of cavitation sometimes occurs naturally in fluid systems and is generally considered undesirable as it contributes to the fatigue and failure of system components.
In addition to micro-organisms, some fluids or fluid systems also have difficulty with larger organisms. For example, the intake canals of power plants are clogged by zebra mussels. These intake canals typically contain large volumes of water, and conventional chemical treatments can prove to be expensive or environmentally unfriendly.
Furthermore, cavitation is also known to be useful in other processes in addition to sterilization of fluids. Cavitation may also be used to sterilize other materials or objects in the fluid; promote chemical reactions (sono-chemistry); treat wood fibers for paper pulp production; de-gas liquids; mix chemicals or slurries; or break down certain compounds.
Therefore, it would be advantageous to develop a method and apparatus capable of sterilizing a large amount of continuously flowing water suitable for use with municipal water supplies, industrial waste water, or utility water supplies. It would also be advantageous to develop such a method and apparatus which utilizes a novel acoustic source rather than traditional transducers. It would also be advantageous to develop such a method and apparatus that is simple and has fewer components. It would also be advantageous to develop such a method and apparatus which efficiently utilizes the acoustic energy. It would also be advantageous to develop a method and apparatus capable of handling larger organisms.
It is therefore an object of the present invention to provide a method and apparatus for sterilizing a large amount of continuously flowing water suitable for use with municipal water supplies, municipal waste water, and industrial food processing waste water.
It is another object of the present invention to provide such a method and apparatus for treating other fluids and/or materials and objects in the fluid; promoting chemical reactions; treating wood fibers for paper pulp production; de-gassing liquids; mixing chemicals or slurries; and breaking down certain compounds.
It is another object of the present invention to provide such a method and apparatus which utilizes a less expensive acoustic source, rather than traditional transducers.
It is another object of the present invention to provide such a method and apparatus which is simple; has few moving parts; and has fewer components and is easily serviceable.
It is another object of the present invention to provide such a method and apparatus which efficiently utilizes the acoustic energy.
It is another object of the present invention to provide a method and apparatus capable of handling larger organisms.
The above objects and others not specifically recited are realized in a number of specific illustrative embodiments of an apparatus and system for treating a fluid and/or materials therein with acoustic energy. For example, the apparatus of the present invention is particularly well suited for sterilizing a continuous flow of water having microorganisms therein by destroying the micro-organisms with induced cavitation. The system includes a vessel for receiving the fluid; a source of condensable vapor, such as steam; vapor headers for equalizing vapor pressure and protecting against liquid backflow; a directional nozzle array for focusing and/or directing acoustic energy; a source of cooling fluid for maintaining subcooled conditions in the vessel; an optional pressurizer or surge tank to either control pressure surges or operation at elevated pressures. The pressurizer option will be dictated by the engineering applications that are involved. Also, for biological applications, an optional heating jacket will be employed to sufficiently heat the vessel walls to retard the growth of organisms which may become attached to the walls.
The vessel has an inner wall defining a chamber. The chamber is configured to allow the fluid to pass therethrough in a continuous stream. The walls of the of the chamber are shaped or curved to focus and/or direct acoustic energy to a particular area of the chamber defining a target zone. The vessel may be elongated and formed of various elongated portions coupled together. The portions may have various cross sectional shapes for focusing the acoustic energy to the common target area. For example, the chamber may be formed by a plurality of portions having partially elliptical cross sections, each with a separate, outer focal point, and a common, inner focal point disposed in the target zone. The vessel may be elongated or create an elongated fluid path to create long enough dwell times such that the target products, such as micro organisms, spend enough time in the acoustic target zone to be destroyed.
The nozzle array has one or more nozzles or spargers coupled to the vessel and directed into the chamber. The nozzle array also has one or more reflector members or shells. The reflector members have a curved wall defining an indentation for focusing and/or directing acoustic energy. The reflector members may have one or a cluster of nozzles directed into the cavity. The indentations or cavities may be parabolic or circular shapes. An individual nozzle cluster and its immediate reflecting shell define a single acoustic source. The shells may have leakage paths, or apertures formed therein, which allow cooling water to circulate about the cavity and maintain subcooled conditions inside the shell.
The nozzles are configured for injecting a condensable vapor into the curved indentations of the reflector members, and thus into the vessel. For example, the nozzle may be a steam sparger injecting steam. The acoustic energy is created by the rapid condensation of the vapor in the presence of the fluid. The acoustic energy is generated by localized water hammer shock waves as vapor bubbles implode. These localized shocks will evolve into large amplitude acoustic pulses that will be focused on the target, or directed at the target zone. Additional acoustic energy may also be induced by local turbulence and mechanical loading on the nozzle and reflector members. This acoustic energy is focused and/or directed at the target zone by the reflector members, and by the inner surfaces of the chamber. The acoustic waves converge with one another in the target zone inducing cavitation. The induced cavitation may be used to treat the fluid or materials therein. The source of the condensable vapor is preferably a steam source supplying waste steam from a utility plant.
Each acoustic source, or steam sparger which its reflector member, is supplied by process steam via thermally insulated steam lines. These steam lines are in turn connected to one or more common steam headers. For most applications, the steam flow in each line will be modulated using off the shelf technology. This modulation can be accomplished with hydraulic valves that area partially opened and closed in a periodic manner. Self modulation schemes may also be employed and will be discussed latersteam lines and associated check valves will be employed to control accidental liquid backflow. The vapor headers equalize the vapor pressure to the various nozzles. In addition, the headers act as a shock absorber in the event of backflow of liquid into the steam pipe.
The cooling system circulates a cooling fluid through the vessel to maintain the vessel, or fluid to be treated, in subcooled conditions. Cooling of the main cavity and the spargers will be done with either pumped bulk flow across the main cavity, or the cooling fluid may be locally injected into the shell cavity of each acoustic source, or a combination of these methods. The coolant may be the same as the fluid which is treated.
For biological applications, the heating jacket surrounds the vessel and heats the walls of the vessel. The jacket may be a secondary, outer shell disposed around the vessel, or it may be a pipe coiled about the vessel. The heating jacket keeps the walls heated to prevent biological growth thereon.
There are several possible geometric configurations for the resonance chamber which house the above mentioned array of acoustic sources, which include but are not limited to cylindrical, spherical, and toridal configurations. The acoustic arrays will focus sonic energy in a target zone of the cavity, where intense cavitation is induced. The cavity walls will help focus this energy by reflecting scattered sound waves that are not directly absorbed in the target region. This target zone will either have no contact or minimal contact with the resonance chamber to minimize cavitation induced wall erosion. Resonate modes that are excited in the cavity will also help to enhance cavitation in the target zone. However, there will be cases where unwanted resonate modes impinge directly on the cavity walls and are too intense. In these situations, baffles will be used to scatter sonic energy to limit localized wall cavitation erosion.
In addition, one or more individual acoustic sources described above can be used for stand alone applications. Each sparger, or nozzle cluster, encased inside its reflecting shell along with its insulated process steam supply line and cooling water intake line, if needed, can be placed in some pre-existing hydraulic structure like an intake canal to power plant or water treatment facility. As an example, the stand alone acoustic source or sources could be used to destroy organisms that clog the intake filters to these facilities.
Finally, for specialized applications that are primarily non-biological, the cavitation chamber can be adapted to operate at elevated pressures with the use of off the shelf pressurizer technology If the in flowing and out flowing liquid to the chamber is isolated form the open atmosphere, and the system is connected to a pressurizer, it is possible to increase the ambient chamber pressure by several hundred atmospheres. An added benefit of using a pressurizer (even at low pressure) is that this system absorbs large amplitude pressure pulses that may otherwise cause pipe and/or vessel ruptures. At elevated pressures, the attendant increase in cavitation implosion energy can increase aby as much as two orders of magnitude.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the invention without undue experimentation. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.